This proposal aims to define mechanisms of T cell tolerance induced in vivo in NZB/NZW Fl lupus-like mice lupus by administration of a novel, artificial peptide (consensus peptide, pCONS). Tolerance results in dramatic delay in appearance of high titer IgG anti-dsDNA and nephritis, and prolongs life 7 months or more. PCONS is constructed from an algorithm based on spontaneous proliferation of BWF1 T cells to wild peptides from the VH regions of BWF1 monoclonal antibodies to DNA. The algorithm predicts amino acid sequences likely to stimulate BWF1 T cells. A wild peptide (p33B) sharing 10 of 15 amino acids withpCONS, representing a sequence in the VH region (CDR1/FR2) of a mAb BWF1 IgG2a anti-dsDNA, has similar effects. Treatment with an artificial peptide that violates the algorithm, pNEG, produces no clinical benefits. Mice treated with pCONS or p33B, but not saline or pNEG, have reduced proliferation of T cells to immunization with the tolerizing peptide, and reduced T cell help for production of IgG anti- dsDNA in vitro. They also fail to develop the high plasma levels of IFN( and IL-4 that characterize saline-treated BWF1 females. We hypothesize that the large effects of these tolerogens result from induction of apotosis, cytokine deviation, or both in a large population of helper T cells - possibly a population that recognizes different peptides from multiple autoantigens, either early in life or later, after determinant spreading. These effects may correlate with affinity and stability of peptide/MHC Class n binding. The hypothesis will be tested by determining peptide/Class II binding affinities and stability (including peptide variants), developing surrogate rapid measures of effects on BWF1 T cells that predict clinical efficacy of peptides with different MHC binding characteristics, determining the effect of peptide/MHC engagement of TCR on T cell survival and cytokines, and testing peptide variants in vivo for clinical effects. Differences between the T cell responses to peptide/MHC complexes in BWF1 and normal mice expressing the MHC Class II molecules restricting these peptides, will identify novel characteristics of Th activation that characterize the autoimmune mice. Since patients with SLE have T cells that recognize Ig-derived peptides from humanmonoclonal antibodies to DNA, the information from these experiments may suggest a novel therapeutic approach to this disease.